The present invention pertains to elongated medical instruments adapted to be permanently or temporarily implanted in the mammalian body or used to access a site in the body to facilitate introduction of a further medical device, and particularly to methods and apparatus for deflecting the distal end and imparting curves in distal segments of such medical instruments within the body by manipulation of a proximal segment of the instrument outside the body.
A wide variety of elongated medical instruments that are adapted to be permanently or temporarily implanted in the mammalian body, usually the body of a human patient, or used to access a site in the body to facilitate introduction of a further medical device. Such elongated medical instruments have an instrument body extending between instrument body proximal and distal ends, and a distal segment of the instrument body is advanced to a remote site in the body by manipulation of a proximal segment of the instrument body or a handle or stylet or the like extending from the instrument body proximal end located outside the body.
Elongated medical instruments include implantable medical electrical leads, catheters, guide wires, and the like. In the case of a medical electrical lead, the lead body proximal end is coupled to an implantable pulse generator (IPG) or monitor that is then implanted subcutaneously or to an external medical device located outside the body and electrical signals are conducted to or from the remote site in the body through one or more lead conductor. Catheters typically extend through the patient""s skin and are coupled with external diagnostic or therapeutic equipment or are used to introduce other elongated medical instruments or fluids or the like, or to withdraw fluids or measure pressure, or the like, through a catheter lumen open at the accessed remote site. Certain catheters, e.g., electrophysiology ablation and mapping catheters, also deliver electrical energy or conduct electrical signals of the body. Other catheters include pulmonary artery catheters, central venous catheters, diagnostic coronary catheters, intra-aortic balloon pump catheters, balloon tipped (PTCA)/angioplasty catheters, and cardiac stent delivery catheters. The terms xe2x80x9ccatheterxe2x80x9d and xe2x80x9cleadxe2x80x9d are often interchanged in these and other contexts. Guide wires are small diameter wires that are directed through tortuous pathways to provide for advancement of medical leads or catheters over-the-wire. Certain guide wires are also designed to function as a micro-catheter for infusion of fluids through a guide wire lumen. Other guide wires include insulated electrical conductors connected at the guide wire proximal end with an external medical device to deliver electrical energy for tissue stimulation or to conduct electrical signals of the body to the external medical device. Hence, in the following discussion, the terms electrical medical leads, catheters and guide wires comprise and can be used interchangeably with elongated medical instruments.
In many cases, the introduction of such elongated medical instruments to a remote site in the body is effected through a skin incision accessing an incision into a blood vessel, whereby the instrument body is advanced through a vascular pathway until the distal segment or the instrument body distal end are located at the remote site. Such advancement is often through a tortuous pathway having twists and turns requiring the capability to impart a curve or deflect the instrument body distal end to facilitate advancement. Therefore, the introduction of such elongated medical instruments through vascular pathways or other tortuous pathways in the body is facilitated by a wide variety of techniques and mechanisms that have been developed to impart curves in the distal segment of the instrument body or to deflect the instrument body distal end.
Currently, during the implantation of a permanent cardiac pacemaker or an implantable cardioverter/defibrillator (ICD), endocardial cardiac leads, e.g., pacing leads and/or cardioversion/defibrillation leads, are introduced into a vein either via a cut down or percutaneous sheath introduction. The cardiac leads are advanced under fluoroscopy into either the right atrium, right ventricle (or both in the case of a dual chamber pacemaker or ICD implantation) or into a cardiac vessel, e.g., the coronary sinus and great vein. Generally speaking, it is highly desirable that such cardiac leads be so flexible through their length that they are capable of flexing with the movement of the heart and other muscular movement so as to void the fracture of the lead body due to its cumulative stressing. Such cardiac lead bodies are generally too limp to be advanced axially on their own through the vascular pathway to the desired site in a heart chamber or vessel. It has been commonplace for many years to employ thin wire stiffening stylets extended down a lumen of the lead body to stiffen the entire assembly so that it can be pushed axially through the venous pathway. Then, the distal pace/sense electrodes or cardioversion/defibrillation electrodes (herein xe2x80x9ccardiac electrodesxe2x80x9d) must be fixed at the preferred site in the heart chamber or vessel to operate most efficaciously and to prevent dislodgement. The introduction and fixation of these cardiac leads is the most time consuming and difficult aspect of the implantation.
At the outset, a straight or slightly curved stiffening stylet is first extended into the lead body lumen within the cardiac lead in order to give the cardiac lead sufficient column strength and rigidity to be pushed through the tributary veins and typically into the subclavian vein. The stylet may be left straight or provided with a certain degree of curvature to facilitate the introduction through these veins and through the initial curvatures thereof. Thereafter, and from time to time, as the physician directs the distal tip of the cardiac lead in a tortuous path leading to the right heart through the superior vena cava (SVC), it may be necessary to withdraw the stylet and either substitute a new stylet or impart a different curvature to the distal portion of the stylet, reinsert the stylet, and advance the distal portion of the lead a bit further until another obstacle to advancement is encountered.
When the distal cardiac electrodes are to be placed in the right ventricle, the physician manually fashions a curve at the tip of another stylet that is inserted into the lead body lumen to advance the assembly through the tricuspid valve into the right ventricle. Most physicians continue advancing the lead with the curved tip stylet in place into the pulmonary artery outflow track to confirm right ventricle access and to rule out the possibility of entrance into the coronary sinus or coronary vein, which can mimic the appearance of a right ventricle placement under fluoroscopy. The conventional practice requires the physician to then remove the curved stylet and partially re-advance the original or another straight stylet into the lead body lumen, once the physician has confirmed that the lead is in fact in the pulmonary outflow track. The cardiac lead is then carefully pulled back under direct fluoroscopic observation until the lead body distal segment drops from the proximal portion of the pulmonary artery to the floor of the right ventricle. The physician then advances the stylet to its fully advanced position within the lead body lumen and advances the lead distal end into the right ventricular apex. Passive or active fixation mechanisms at the lead body distal end then effect fixation with the trabeculae or the myocardium to acutely maintain the cardiac electrode electrode(s) at the operative site.
In the case of atrial lead placement, the lead body distal end is typically lodged or affixed in the right atrial appendage which results in the lead body extending into the right atrium via the SVC and then bent through about a 180xc2x0 or greater bend.
Over the years, many atrial cardiac lead designs and atrial cardiac lead introduction tools and techniques have been proposed or clinically used to both achieve this orientation and to fix the cardiac lead body distal end within the atrial appendage and avoid dislodgement. Initially, such atrial cardiac leads were formed with a permanent xe2x80x9cJxe2x80x9d-shaped bend to facilitate both the positioning and the retention of the atrial electrode in the patient""s atrial appendage as taught, for example, in U.S. Pat. No. 4,136,703. Insertion of these xe2x80x9cJxe2x80x9d-shaped leads is greatly facilitated through the use of a straight solid inner stylet which, in this case, straightens the bend normally fixed within the distal end of the lead itself to the extent that the stylet is advanced into or retracted from the lead body lumen.
Moreover, it has been proposed to combine atrial and ventricular leads together or in a cooperative relation to provide a xe2x80x9csingle passxe2x80x9d implantation of both leads as set forth in U.S. Pat. Nos. 4,458,677 and 4,479,500 and patents referenced therein. Such proposed single pass AV leads have not gained acceptance due to their complicated construction, use and size.
J-shaped atrial leads have largely been abandoned in favor of reduced diameter lead bodies that cannot accommodate shape-forming structures and the use of the straightening stylet as described above. Today, the small diameter cardiac lead body is normally straight, and the lead body distal end is typically aimed into the atrial appendage employing multiple insertions of relatively straight and curved stylets. The electrode bearing lead body distal end is fixed in the atrial appendage by means of an active fixation screw or passive fixation tines. However, dislodgements can occur before the fixation is effected when a stylet is withdrawn proximally as the stylet may bind against the lead body lumen in the region of the bend.
Thus, there are multiple exchanges of straight stylets and curved stylets which have been bent according to the physician""s choice in a typical cardiac lead implantation in the right atrium and ventricle. Similar techniques and multiple stylets are avoided to advance a cardiac lead distal segment into the coronary sinus and great vein. Stylets are typically formed of solid wire, typically about 0.014-0.018 inches in diameter. During handing, such stylets can easily become bent or kinked, and thereafter cause great difficulty when an attempt is made to reinsert them through the narrow inner diameter of the lead body lumen, which may only be 0.019 inch in the case of a stylet of 0.018 inch diameter, thereby providing no more than 0.0005 inch clearance around the circumference. The continual withdrawal and reintroduction of stylets is time consuming and offers the potential of damaging the lead in the process.
Moreover, it is undesirable to contaminate the lead body lumen with blood during this process because drying blood can form a strong adhesive bond between the stylet and the lumen wall, making stylet removal impossible and rendering the lead unusable. Because the surgeon is working through an open wound, even the most fastidious surgeon will have blood on his gloves that can be transferred to the stylet. The blood congeals, and because of the small clearance, even a few drops of blood are sufficient to causing jamming of the stylet inside the lead body lumen. When the stylet jams in the lead body lumen, kinking of the stylet within the lead can occur, which kinks, in turn, will create new jams or problems with the insertion and retraction of the stylet from the lead body lumen. In some cases, the jamming is so severe that the cardiac lead must be removed from the heart for fear of insulation puncture, discarded, and a new lead implanted, thereby at least doubling the lead cost used in the procedure as well as operative time. The overall result of such difficulties is that operative time is greatly increased which results in increased time delay, associated cost, and prolonged X-ray exposure to the patient under continuous fluoroscopy as well as prolonged scattered X-ray exposure to the operating room staff due to procedural time delays. These problems with the use of multiple stiffening stylets have been recognized in the art as set forth in U.S. Pat. Nos. 4,136,703, 4,381,013, 4,677,990,5,662,169, 5,824,031, and 6,059,739, for example.
Many proposals have been advanced to reduce the number of stylets and the consequent number of times that stylet removal and re-insertion that are needed in the procedure. One approach has been to employ deflectable stylets wherein the stylet distal segment can be deflected or curved while within the lead body lumen from the proximal end thereof. Two-piece stylets that comprise a straight, tubular outer member and a curved inner member received within the outer member lumen enabling relative movement of the inner and outer members are disclosed in the above-referenced ""703 and ""013 patents for straightening a J-shaped bend and in U.S. Pat. No. 5,728,148. The outer tubular member of the ""013 patent enables the transmission of torque applied by the implanting physician at the proximal end to be transmitted to a fixation helix located at the lead body distal end lead to screwed the helix into endocardial tissue. Alternatively, two-piece stylets comprising a curved outer member and a relatively straight inner member are also known to the art, as disclosed in U.S. Pat. Nos. 4,676,249 and 5,040,543. In such composite stylets, the relative position of the inner member with respect to the outer member determines the degree to which the curved member (inner or outer) is allowed to display its preset curvature.
A commonly employed approach to providing controllable deflection of the distal end segments of catheters and guide wires employs a generally straight outer sheath and a pull or push or push-pull wire extending through a lumen of the outer sheath to an attachment point at the sheath distal end. The wire is pushed or pulled on at its proximal end typically through a handle that is permanently or removably attached to the catheter or guide wire proximal end. The proximal retraction or distal advancement of the pull or push wire, respectively, causes at least a distal segment of the outer sheath to bend or deflect. Examples of such deflection mechanisms in catheters can be found in U.S. Pat. Nos. 4,815,478, 4,898,577, 4,940,062, and 5,545,200. U.S. Pat. Nos. 4,815,478 and 4,940,062 disclose the use of push-pull wires extending through guide wire lumens for deflecting the guide wire distal end by manipulating a handle at the guide wire proximal end. Deflectable stylets intended to be inserted into cardiac lead body lumens employing this type of deflection mechanism are disclosed in U.S. Pat. Nos. 5,662,119, 5,170,787, and 5,327,906, 5,439,006, and 6,059,739.
The above-referenced ""990 patent discloses the combination of a removable stylet and at least one non-conductive thread that function like a pull wire having very low elasticity coupled near the cardiac lead body distal end or at selective locations along the lead body. The thread extends from the lead body lumen proximal end opening through a proximal segment of the lead body lumen and then is passed through the turns of the lead conductor coil and extends distally through a distal segment alongside the conductor within the lead body sheath to the distal attachment point outside the conductor whereby the thread axis is offset from the coiled wire conductor axis. The cardiac lead is introduced into the right atrium with the straight stylet inserted in the lead body lumen alongside the thread. A curvature is induced in the lead body distal segment by applying traction to the thread proximal end exiting the lead body proximal end opening thereby pulling the thread taut and proximally. The curvature is dictated by the length of the distal segment where the thread extends in the space between the outer insulation sheath and the coiled wire conductor. The stylet is described as having portions of reduced thickness along a distal segment parallel with the distal segment of the lead body where the thread extends outside the lead body lumen to achieve easier bending. The ""990 patent addresses concerns raised by the conventional technique of withdrawing, imparting a new curve, and reinserting the stiffening stylet during the implantation procedure. However, the stylet could bind in the lead body lumen with the thread upon retraction of the stylet and dislodge the lead body distal end segment. Also, the thread must be cut off before the lead body proximal end is attached to the IMD, rendering it inaccessible and presenting an obstacle to reinsertion of a stylet should that become necessary at some point later in the procedure or during the chronic implantation to correct a dislodgement or to remove the cardiac lead.
Moreover, the physician is required to employ both hands in order to manipulate the separate thread, the stylet extending proximally from the lead body lumen in the ""990 patent and to hold the lead body proximal end steady. Similarly, the physician usually uses two hands to manipulate the deflectable stylets and the two-piece stylet of the ""013 patent, for example, as well as the conventional one-piece stylets. It is usually necessary to manipulate the lead and stylet to advance and withdraw the stylet and rotate the lead body in the advancement of the lead body through the venous pathway and the lead body distal end into particular desired sites for lodging the electrodes.
Single-handed manipulation of such elongated medical instruments has been proposed but usually requires use of a bulky handle that enlarges the overall diameter of the instrument at the proximal end For example, U.S. Pat. No. 3,452,740 discloses a spring guide manipulator for imparting a curvature and rotation in a spring guide by one-handed use of a manipulative handle. The spring guide wire includes the conventional inner straight wire coupled to the distal end of the coiled wire of the distal portion of the spring wire guide. When the handle is attached to a guide wire and a catheter is fitted over the guide wire, it is reported that the handle may be employed to both rotate the guide wire and catheter as well as place a curve in the distal portion of the catheter. The above-referenced ""662 and ""739 patents as well as U.S. Pat. No. 5,170,787 disclose steerable stylets particularly for use in cardiac lead body lumens for selectively adjusting the curvature of the lead body that are manipulated by one hand operation, but are relatively complex and costly.
While all of the mechanisms disclosed in the above cited prior art patents are at least to some degree workable, there is still a perceived need for a mechanism that is simple, inexpensive to manufacture, does not excessively increase the elongated medical instrument body diameter, and can be manipulated using one hand to control the deflection and imparted curvature of the instrument body distal segment
More significantly, there is a need for a such a mechanism that eliminates the need for separate curved stylets used to deflect and impart curves in the medical instrument distal segment and which provides a wide degree of dynamic curvature to the elongated medical instrument being advanced by the physician.
The invention is therefore directed to improvements in such elongated medical instruments that eliminate the need for separate stylets used to deflect and impart curves in the instrument distal segment and wherein the degree of deflection and curvature can be controlled using one hand.
In accordance with the present invention, the elongated medical instrument comprises an instrument body extending a predetermined length between instrument body proximal and distal ends and enclosing an elongated, inelastic, pull wire extending between a pull wire proximal end affixed at a point at or near the instrument proximal end and a pull wire distal end affixed at or near the instrument body distal end. The pull wire extends through a pull wire lumen that is off axis in a radial direction from the medical instrument axis and through a distal segment of the lead body that is to be curved so as to deflect the instrument distal end. The instrument body is formed of an elastic material at least in a proximal segment thereof that can be stretched or extended axially when tension is applied between proximal and distal ends of the proximal segment so as to increase the length of the proximal segment from its relaxed length. The applied tension is transferred to the inelastic pull wire which counters the extension of the proximal segment by bending the instrument body distal segment in the radial direction away from the instrument body axis. The proximal segment can either be xe2x80x9cin-linexe2x80x9d with the distal segment or can be formed as a side arm or branch of the proximal portion of the lead body that remains outside the body during implantation.
The elongated medical instrument further comprises a stylet lumen that extends from a stylet lumen proximal end opening at the instrument body proximal end to a stylet lumen distal end at the instrument distal end or in the instrument body distal segment. A stiff, straight stylet is introduced through the stylet lumen so that the degree and length of curvature induced in the distal segment depends upon the length of the stylet advanced through a proximal portion of the distal segment while tension is applied to the proximal segment. The stylet lumen is preferably offset radially from the lead body axis and 180xc2x0 displaced from the pull wire lumen and pull wire.
Preferably, the proximal segment is adapted to be fitted into a hand-held tool that engages the proximal and distal ends of the proximal segment and applies a selective amount of tension that stretches the proximal segment from its relaxed length upon manual manipulation of the hand-held tool. Distance limiting stops that limit the maximal lengthening of the proximal segment and force limiting springs are preferably formed in certain of the hand-held tools
Preferably, the distal segment of the instrument body is formed of a relatively inelastic material that resists axial stretching or contraction, and the proximal segment is formed of a more elastic material that is capable of elastically stretching axially over the maximal length of the proximal segment without any damage. The distal segment may compress axially slightly when the proximal segment is stretched axially.
One preferred embodiment of the elongated medical instrument comprises a cardiac lead particularly adapted to be placed in the right atrium or in the coronary sinus or the right ventricle for cardioversion/defibrillation and/or pacing in the right atrium or in the coronary sinus or in the right ventricle, respectively. In a unipolar embodiment, the lead conductor extending between a proximal connector pin and a distal cardiac electrode is preferably formed of a loose wound coiled wire fitted within the stylet lumen. The stiffening stylet extends through the coil lumen, and the coil turns are capable of stretching and compressing axially within the stylet lumen as the proximal segment is stretched and returns to its normal relaxed length.
In one bipolar or multi-polar embodiment, wherein one or more additional distal cardiac electrode and proximal connector element are coupled together by a respective lead conductor, the pull wire can be attached to and function as the lead conductor between a respective connector element and cardiac electrode.
In a further preferred embodiment, the present invention is implemented into a single pass AV lead for pacing and/or cardioversion/defibrillation comprising atrial and ventricular lead bodies combined together through an intermediate segment thereof. The proximal segment of the atrial lead branching from the intermediate segment is formed in accordance with the invention, and the permanently enclosed pull wire extends through the atrial lead body and may constitute an atrial lead conductor. The ventricular lead body accepts a removable stiffening stylet.
This summary of the invention has been presented here simply to point out some of the ways that the invention overcomes difficulties presented in the prior art and to distinguish the invention from the prior art and is not intended to operate in any manner as a limitation on the interpretation of claims that are presented initially in the patent application and that are ultimately granted.